Eco uses language on client and on the server, e.g. the two can have differing languages which means that the server displays server-side stuff in the language that was configured for it. You can change the language for the server in /steamapps/common/Eco/Eco_Data/Server/Configs/Localization.eco, just enter "German". If you're not the admin, you would need to ask the admin of the server if he is willing to do that.
Looks like this issue: https://github.com/StrangeLoopGames/EcoIssues/issues/23109
It's being investigated.